This invention relates to a fluid pressure actuator and more particularly to a fluid pressure actuator comprising a cylinder containing a shaft rotatable by a fluid pressure, the cylinder per se preferably being adapted to expand and contract.
The fluid pressure actuator according to this invention is operable by hydraulic pressure or pneumatic pressure, and drive for a piston member thereof may be the single-acting type or the double-acting type.
Hydraulic rotary motors are broadly classified into vane system motors and piston system motors. The piston system motors include the rack and pinion type, the helical spline piston type, the piston chain type and the piston link type.
What is the closest to the fluid pressure actuator of this invention is the helical spline type, which has such a construction that, when a hydraulic pressure is applied to slide a piston mounted in a cylinder body, a helical spline slidable in unison with the piston imparts a rotational force on a helical spline in engagement therewith and rigidly attached to a rotary drive shaft. This helical spline piston type allows length of the helical splines to be determined freely and therefore the angle of rotation to be selected as desired. On the other hand, it has problems of requiring a great driving energy, of involving considerable energy losses and of its operation tending to be heavy.
A known actuator providing a rotational movement, and expansion and contraction or linear movements generally utilizes a cylinder to carry out the expansion and contraction. However, it can be said that the cylinder and a rotary part are in a very poor degree of organic combination. Therefore, its entire construction very much tends to be large, heavy and complicated. Such a known actuator also has a problem from a point of view of balance, and often loses smoothness of operation.